The present invention is related generally to processes for the manufacture of roof coverings, and more particularly to a process of controlled heating of a coating material for a roof covering.
Processes for the manufacture of roof coverings, such as roofing shingles or roll roofing, usually include a step of applying a molten coating material to a substrate, followed by a step of applying roofing granules to a surface of the coated substrate. In a typical process, the coating material is a mixture of asphalt and a filler such as ground limestone. The filler is heated before mixing it with heated asphalt to form the molten coating material. In most processes, the filler is heated by passing it through a filler heater that uses a fluid such as heated oil as a heat exchange medium.
Increasing the temperature of the molten coating material reduces its viscosity. It is desirable to maintain the viscosity of the molten coating material within a predetermined range when it is applied to the substrate, to insure good coating of the substrate and good application of the granules. At times, the continuous manufacturing process may be slowed down or stopped intentionally or unintentionally for various reasons. During such times, the filler remains inside the filler heat longer than usual. The increased heating may cause the temperature of the filler to increase above a desired temperature. When the overly heated filler is mixed with the asphalt, the temperature of the resulting coating material may be too high and the viscosity of the coating material too low. As a result, it may lead to processing problems, quality problems, or even to scrapping the resulting product. Therefore, it would be desirable to provide a process to control the heating of the filler during slowdown or stoppage of the process, in order to control the viscosity of the coating material. The resulting improvement in consistency of the filled coating viscosity may lead to improved consistency in granule penetration and, therefore, improved aesthetic properties of the roofing shingles, such as a reduction in shading.
U.S. Pat. No. 3,857,552 to Ohlson discloses a process of making an asphalt concrete mix, in which a mineral aggregate for the concrete mix is heated in a heating drum by use of an oil burner. The oil burner can be adjusted to a desired heating temperature by adjusting the supply of oil to the burner. However, there is no suggestion to heat the aggregate using a heat exchange medium, and no suggestion to cool a heat exchange medium in order to maintain the temperature of the aggregate below a predetermined level.
U.S. Pat. No. 4,475,818 to Bialkowski discloses a process of making an asphalt coating mix, in which the ratio of limestone to asphalt in the mix is adjusted to control the viscosity of the mix. During the process, the limestone is heated in a heating chamber, but there is no suggestion to heat the limestone using a heat exchange medium. Further, there is no suggestion to cool a heat exchange medium to maintain the temperature of the limestone below a predetermined level.
The above object as well as others not specifically enumerated are achieved by a process to control the heating of a coating material for a roof covering according to the invention. The coating material is heated using a heat exchange medium in a continuous process. The heat exchange medium is cooled in response to a slowdown or stoppage of the continuous heating process to maintain the temperature of the coating material below a predetermined level.
In another embodiment, the invention relates to a process to control the heating of a coating material for a roof covering. The coating material is heated to a first coating material temperature using a heat exchange medium at a first flow rate of the coating material. The temperature of the heat exchange medium is adjusted to accomplish a second coating material temperature at a second flow rate of the filler, where the second flow rate is less than the first flow rate.
In another embodiment, the invention relates to a process to control the viscosity of an asphalt coating for a roof covering. A filler for the asphalt is heated to a first filler temperature using a heat exchange medium at a first flow rate of the filler. The temperature of the heat exchange medium is adjusted to accomplish a second filler temperature at a second flow rate of the filler, where the second flow rate is less than the first flow rate.